Obstructive sleep apnea syndrome (OSAS) is a common disease and an important public health problem. The etiology is poorly understood and quality research is limited. OSAS is associated with an increased incidence of myocardial infarction, cerebrovascular accidents, hypertension, and congestive heart failure. OSAS causes daytime fatigue and poor work performance. For instance, fall-asleep car accidents have become more common than alcohol related accidents. It is estimated that 98% of adults with OSAS lack specific upper airway pathology, such as neoplastic lesions or metabolic enlargement of pharyngeal soft tissue. Thus, the cause of most obstruction is not known. Research evaluation of the upper airway for both pre- and post-operative patients is needed to determine the specific change in airflow and anatomy. Few studies have analyzed the anatomic outcome for OSAS treatment. It is difficult to compare and predict the 3-dimensional anatomy in patients with OSAS. Clinicians assume treatment modalities increase the upper airway but scientific evidence is poor. The computer-aided engineering (CAE) plays an important role in the engineering community for design, analyses, and performance predictions. CAE provides the computational engineers with computing resources that were unimaginable just a decade ago. The Computational Fluid Dynamics (CFD) and associated enabling technology in high-fidelity computational simulations facilitate numerical geometry modeling, numerical mesh generation, flow field simulations, scientific visualization, and high-performance parallel computing. These applications can greatly help medicine to understand the dynamics and behaviors of a human body as well as design of medical treatment. This proposal is to utilize CFD to predict the presence, severity, and outcomes of OSAS by using computed tomographic scans and polysomnography data of adult obstructive sleep apnea patients following maxillomandibular advancement. Our goal is to more accurately identify the anatomical changes in the airway following surgery and improve presurgical prognosis. Project Narrative: Obstructive sleep apnea syndrome (OSAS) is a common disease and an important public health problem. These applications can greatly help medicine to understand the dynamics and behaviors of a human body as well as design of medical treatment.